This invention relates to an exhaust system for a watercraft and more particularly to an improved high efficiency exhaust system that provides effective silencing with minimum back pressures.
It is well known that the control of the noise from engines that power watercraft presents significant problems. The reason for this is that the watercrft normally has a relatively limited area available for silencing devices. Thus, it is difficult to provide effective exhaust silencing for the exhaust gases of the powering internal combustion engine in a watercraft.
One way in which the watercraft exhaust gases are silenced is by discharging the exhaust gases or a portion of them below the level of water in which the watercraft is operated. In this way, the body of water acts as a silencing device.
Such arrangements, however, have several disadvantages. First, in planing type watercraft, the degree of submersion of the hull varies with the speed of travel. Thus, an exhaust discharge may be under water under some speeds but above water under other speeds. Thus, the silencing under all running conditions is difficult. Also, if the exhaust outlet is disposed so that it is under water under all running conditions, then, when the watercraft is travelling slowly, the discharge is so deeply submerged that the back pressure on the engine is too high.
In addition to these problems, there is also a danger that water may enter the engine through the exhaust system. This is obviously undesirable. Therefore, it is also the practice to employ water trap devices in the exhaust system for insuring against water intrusion into the engine. However, when the exhaust system outlet is submerged, the water trap devices may not be capable of totally protecting the engine.
In some type of watercraft, such as jet propelled watercraft, the jet propulsion unit is disposed in a tunnel that is formed on the underside of the hull and toward the rear of the hull. It has been the proposed to discharge the engine exhaust gases into this tunnel either above, at or below the water level therein. Where the discharge is below the water level, the aforenoted problems can occur. Where the discharge is above the water level, the tunnel itself may at times act as a resonating chamber and can actually amplify the noises rather than dampen them.
It is, therefore, a principal object of this invention to provide an improved exhaust system for a watercraft.
It is a further object of this invention to provide a watercraft exhaust system that provides effective silencing under all running conditions while insuring against water intrusion into the engine through the exhaust system.
It is a further object of this invention to provide an improved exhaust system for a watercraft wherein the exhaust gases are discharged into a tunnel in which the watercraft propulsion unit is contained but the exhaust gases are effectively silenced.